Depth, with a number attached
Three feet from the wall to twelve, and the shot 'easily triples' in depth.
Depth is what separates a scene that feels three-dimensional from one that reads flat, and four techniques produce it: a low aperture to blur the background, physical separation between subject and background, a foreground layer - 'three layers of depth is greater than two' - and leading lines that both show distance and pull the eye. The version worth remembering is the measured one from the budget lighting demo, where moving the subject from about three feet off the wall to twelve or thirteen roughly triples the perceived depth without changing a single setting. The same principle then reappears in lighting, where a backlight is called 'the number one thing that gives you this power' to separate a subject in space.
Turns an abstract rule into a distance you can pace out on set.
Three layers of depth is greater than two.